ADC 0808/0809 Interfacing With 8051 Microcontroller

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ADC 0808/0809 Interfacing With 8051 Microcontroller
In physical world everything is analog/continuous ( pressure, temperature, velocity, humidity etc ). ADC (analog to digital converter) is a way used to convert any physical data which is in analog to the format microcontroller can read and process them. We will need a device to display the output here we are using LCD for that purpose. We will also need some input to feed as analog signal, here we will use potentiometer.



ADC0808/0809 Chip with 8 analog channels:

·       Manufactured by National semiconductor
·       Allows to monitor 8 analog inputs
·       8 bit data output

Pin Description:

·       ADDRESS LINE A, B, C
The device contains 8-channels. A particular channel is selected by using the address decoder line. The TABLE 1 shows the input states for address lines to select any channel.

·       Address Latch Enable ALE
The address is latched on the Low – High transition of ALE.

·       START
The ADC’s Successive Approximation Register (SAR) is reset on the positive edge i.e. Low- High of the Start Conversion pulse. Whereas the conversion is begun on the falling edge i.e. High – Low of the pulse.

·       Output Enable
Whenever data has to be read from the ADC, Output Enable pin has to be pulled high thus enabling the TRI-STATE outputs, allowing data to be read from the data pins D0-D7.

·       End of Conversion (EOC)
This Pin becomes High when the conversion has ended, so the controller comes to know that the data can now be read from the data pins.

·       Clock
External clock pulses are to be given to the ADC; this can be given either from LM 555 in astable mode or the controller can also be used to give the pulses.

ALGORITHM:
1.     Start
2.     Select the channel
3.     A Low –High transition on ALE to latch in the address
4.     A Low – Low transition on start to reset the ADC’s SAR
5.     A High – Low transition on ALE
6.     A High – Low transition on start to start the conversion.
7.     Wait for End of cycle (EOC) pin to become high.
8.     Make Output Enable pin High.
9.     Take Data from the ADC’s output
10.    Make Output Enable pin Low.
11.    Stop



Embedded C Code:
#include<reg51.>
sbit ALE=P2^4;
sbit OE=P2^5;
sbit SC=P2^6;
sbit EOC=P2^7;
sbit ADDR_A=P2^0;
sbit ADDR_B=P2^1;
sbit ADDR_C=P2^2;
sfr MYDATA=P1;
void main()
{
 unsined char value;
 MYDATA=0xFF;
 EOC=1;
 ALE=0;
 OE=0;
 SC=0;
 wile()
 {
   ADDR_C=0;
   ADDR_B=0;
   ADDR_A=1;
   MSdelay(1);
   ALE=1;
   MSDelay(1);
   SC=1
   MSDelay(1);
   ALE=0;
   SC=0;
   while(EOC==1);
   while(EOC==0);
   OE=1;
   MSDelay(1);
   value=MYDATA;
   OE=0;
   ConvertAndDisplay(value);
   }
   }

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